how to turn off constrain proportions? Trying to resize and image...

I am trying to resize an image in Pages and the constrain proportions box is checked and greyed out so I cannot un-check it. Currently, when I try to change the image size by clicking on the little corner squares, the image disappears and the size is 92 width and 98 height. When I try to change the numbers manually, it goes back to the huge image size... I have no idea what to do and Pages Help is not helpful. And of course I have a deadline, please help!